of tobbington



March 8, 1932. G. R. TRUMBULL 1,848,757

FUSE PLUG Filed Aug. 2. 1930 I -L 7 l 3 2 mm x 1 7 42011117 l 1 the fuse at a definite point when subjected particularly Patented Mar. 8, 1932 UNITED STATES PATENT OFFICE GIDBGE B. TBUHBULL, Oil? TORRINGTON, CONNECTICUT, ASSIGNOB TO BULLS-m ELECTRIC MANUFACTURING COMPANY, OF TOBBUGTON, CONNECTICUT, A COB- IORATION OI CONNECTICUT FUSE PLUG Application filed. August 3, 1980. Serial No. 472,814.

My invention relates to improvements in electric fuse plugs.

One object is to provide a reliable but cheap fuse with markings which are clearly visible. 6, to indicate the rating when it is in normal condition for use and which will also clearly indicate when it has blown.

Another object is to prevent the formation of gases within such a fuse in sufficient l quantity to generate an explosive pressure within the fuse body.

Another object is to prevent heat generated by arcing of the fuse at the instant of rupture from causing failure of the enclosing top.

Another object isto provide for failure of to its rated overload of current.

My invention is applicable to types of electrical fuse plugs having transparent tops and to those of the screw mounted type in WhlCh the top ismade of glass. Experience has shown that when the fuse is ruptured by an overload the heat and gas pressure enerated frequently cause breakage of the glass or other housing with consequent damage to surrounding objects and personal injury.

The intensity and duration of the arc in the fuse depend somewhat upon the amount of oxygen in the air adjacent to the ruptured terminals. By filling the space within the fuse body which usuall contains air with an inert and incombusti le powder, such as lime, it is possible to greatly reduce the quantity of air and consequently of oxygen there Also by reducing the cross section of the fuse link to cause it to failunder its ratedf point and imbedding overload at a definite that point and the adjacent portions ofthe fuse in an inert, non-conducting solid mass, such as sodium silicate or water glass, within the top, the air in the fuse chamber is further reduced in volume and excluded from the point of rupture. Since the form of sodium silicateused is transparent, suitable marking on the fuse link can be readily distinguished through it. As it fills the interval between the glass top and the fuse link beneath, there is no chance of the latter becomillilg obscured by infiltration of the powdered When the ordinary air filled'fuse blows, the flame of the arc tends to blacken the interior of the fuse body and make diflicult the determination of the condition of the fuse link, whereas with my invention it has been found that the action of the electric are on the sodium silicate causes it to change from a transparent solid to a white powder which is more readily distinguished as an indication of the failure of the fuse.

Other advantages of my invention will be disclosed in the drawings and description accompanying this application. a

In the attached drawings Fig. 1 is a transverse sectional view of a screw type fuse plug embodying my invention.

Fig. 2 is a front view of the plug.

Fig. 3 is a front view of the fuse Fig. 4 is an inverted view of Fig. 1 showing a modified construction.

ig. 5 is a to view of the apertured paper disc shown in ig. 4.

Fig. 6 is a section on the line 66 of Fi 1, with the filling owder and shell omitte The plug type se illustrated in Fig. 1 has the base 7 and top member 8 of insulating material which fit together to form the chamber for the fuse link 9 imbedded in a protecting layer of transparent sodium silicate or water glass 10. In the preferred form shown the top member is of glass. One end of the fuse link 9 is connected to the terminal 11 which passes through the base 7 and is bent over to form the usual central circuit contact and the other end of the fuse link is connected to the terminal 12 which also passes through the base 7 but is bent away from the center and into contact at 13"with the conducting threaded shell or ring 13. The terminals 11 and 12 may be secured in position by any suitable means, such as by being moulded into the base 7. The contact point 13 may be fastened with solder if desired. The shell 13 also servesto hold the base 7 and the top 8 together.

The chamber within the fuse body between the protective coating 10 and the insulating base 7 is filled with powdered lime 14-, closely compacted around the terminals 11 and 12.

The preferred coating is commonly known water glass. The composition of this may vary considerably but I have found a clarified solution with the proportions of approximately 80% SiO 9% Na O and a specificv gravity of approximately 40 Baum satisfactory.

This may serve as an adhesive or cement to secure the fuse strip to the inner wall of the top and thus completely prevent the lime from working in between the strip and the glass or other transparent top.

[in alternative construction is illustrated in Fig. at in which a perforated disc of paper, 18, is inserted in the glass top above the fuse link having a central hole forming an aperture through which the central portion 16 of the fuse link 9 is visible.

A notch 19 may be formed in the bottom edge of the top member 8 to allow powdered lime to be introduced into the central chamber. This notch is closed by the ring 13 as it is screwed onto the top member.

When the fuse fails or blows on account of circuit overload the fuse link parts at the narrow portion 16 and the heat generated causes the sodium silicate to change from a transparent solid to a white powder which can be readily seen through the transparent top. The powdered lime in the fuse body occupies practically all of the space which would be filled with air in the ordinary fuse of this type, so that there is ver little oxygen present to support arcing com ustion of the severed ends of the fuse hnk, and the'generation of heat and gases is promptly arrested.

The sodium silicate also serves to insulate the glass top against the heat caused by the failure of the fuse.

It is important that the sodium silicate be in direct contact with the upper inner surface of the glass top,;8 and in order to insure this condition I prefer to pour liquid sodium silicate into the chamber in the top 8 in an inverted position to sufiicient depth to just cover the fuse strip 9 in position as shown in Fig. 1. The fuse strip 9 is attached to the terminals 11 and 12 and the latter are moulded in position in the insulating base 7 The strip and base may then be inserted into the chamber in the top member 8 while the sodium silicate is still soft and allowed to stand until it has hardened or set. Powdered lime is then poured into the chamber through the notch 19 until all the remaining space is filled. The threaded ring 13 is next applied over the base 7 and screwed onto the threaded portion of the top member 8 to hold them together, close the notch 19 between them and make contact with the terminal 12 at 13. Solder is finally applied at 13 to prevent the ring 13 from backing off and to perfect its electrical connection with the terminal 12.

In case the paper disc 18 is to be used, it should be placed in its position in the opening before the liquid sodium silicate is introduced.

Other methods of'applying the arc retardent material may be used. The fuse link may be coated with liquid sodium silicate and then laced in position either before or after the iquid has hardened, as may suitthe requirements. The insulating base may be formed with a suitable opening 19' into the central cavity through which the lime may be introduced, and the opening then closed with insulating material such as sealing wax.

The fuse link 9 is marked on its upper surface with suitable current rating designations, such as at 15, which may be of contrasting color from the background on which they are printed. The central portion of the fuse link is narrower than the rest of the link and of.the proper cross section to correspond with its rated current capacity. This central part 16 is also colored or printed in contrast with the adjacent portions of the fuse link and various color combinations may be used to indicate differing capacities, for instance, a red center mark on a lighter back ound.

In order to render the fuse markings more readily distinguishable the central portion of the glass top 8 has a spherical section 17 extending upwardly and forming a magnifying lens causing the parts immediately beneath to appear enlarged when viewed from above.

It will thus be seen that I have provided a cheap and practical device for fusing electrical circuits whereby the heat caused by fuse failure is eatly reduced, continuation of the arcing e ect is prevented and the condition of the fuse is clearly indicated.

I claim:

1. A fuse lu having arc retardant means consistin of; Triable transparent solid and powdere lime.

2. In a fuse plug means for providing visible indication when the fuse has blown, comprising a coating of transparent sodium silicate over the fuse link.

3. A fuse plug having a magnifying transparent top, a fuse link positioned below said top and water glass for providing visible indication when the fuse has blown.

4. A fuse plu having a magnifying glass top, a coatin of transparent sodium silicate adjacent sai top, a fuse link imbedded in said coating, granulated lime below said fuse link and'means for holding the lime inside the plug.

5. In a fuse plug a magnifying glass top, an insulating base, terminals carried in said base, 'a fuse stri connecting said terminals,

a layer of friab e transparent solid material granulated lime filling the space remaining in the plug and a threaded conducting sleeve in electrical contact with one of said terminal:. f 1

6. use p ug comprising a transparent a glass top having a chamber, a fuse link mounted in said chamber and visible through the top, a coating of transparentwater glass on the interior wall of the chamber through which the condition of the fuse link is visible, said coating serving to protect the glass top and serving as an indicator when the fuse blows.

7. A fuse plug having a chambered magnifying glass top member threaded on its lower en a fuse link within said top member, terminals attached to said link, an insulating base adapted to receive said terminals a threaded conducting shell adapted to.

. receive said insulating base and engage the threads on said top member in electrical contact with one of said terminals, a transparent coating of sodium silicate on said fuse link in-contact with the under side of said top 5 member and a filling of powdered lime within said chamber. I I

8. A fuse plug comprising a body formed of two parts havlng a chamber between them, one part having a transparent portion, a 3n shell connecting the parts, a fuse strip in the chamber having rate marking visible through the transparent portion and having terminals one of which is connected to said shell, 2. filling of incombustible powder behind the as marked portion of the fuse strip and means for preventing the powder from getting between the fuse strip and the transparent portion of the body.

GEORGE R. TRUMBULL. 

